Motor Starting and Control Primer: An introduction to the starting techniques and control of electric motors by Steven McFadyen

Author:Steven McFadyen [McFadyen, Steven]
Language: eng
Format: epub
Publisher: Steven McFadyen
Published: 2014-04-24T00:00:00+00:00

Adjustable Starting Parameters

No Break in Motor Supply During Starting

Small Reduction in Peak Current

Resistance Bank Required

Rotor Resistance Starting

Rotor resistance starting, like primary resistance starting, involves the addition of resistors into the external circuit. Unlike primary resistance starting, the resistors are connected into the rotor circuit (for resistor connection into the stator circuit see previous chapter). Rotor resistance starting is more expensive and complex than primary resistance starting due to the requirement of slip rings on the rotor and the switching of resistor banks. However, a significant benefit is that the selection of resistors (torque) can be matched to the mechanical requirement of the load.

During rotor resistance starting, banks of resistors are connected into the rotor circuit at the start. As the motor accelerates the resistor banks are switched out on timers until, at full speed, the motor is running directly connected to the power supply.

In rotor resistance starting the torque is nearly proportional to the line current. For example:

A starting torque of 3 times the normal torque will have a starting current of around 3

times the normal running current.

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